Method for acquiring resource region information for phich and method of receiving pdcch

ABSTRACT

A method of acquiring information on a resource region for transmitting PHICH and a method of receiving PDCCH using the same are disclosed. The resource region for transmitting the PHICH can be specified by first information corresponding to the per-sub frame PHICH number and second information corresponding to a duration of the PHICH within the subframe. The first Information can be specified into a form resulting from multiplying a predetermined basic number by a specific constant. And, the specific constant can be transmitted via PBCH. Moreover, the second information can be acquired from the PBCH as well.

TECHNICAL FIELD

The present invention relates to a method of acquiring locationinformation of a resource region for transmitting a physical hybrid HARQindicator channel (PHICH) in a mobile communication system and a methodof receiving a physical downlink control channel (PDCCH) using the same.

BACKGROUND ART

In transmitting a packet in a mobile communication system, a receivershould inform a transmitter of a presence or non-presence of success ofa packet reception. In case that the packet reception is successful, ACKis transmitted to enable the transmitter to transmit a new packet. Incase that packet reception fails, NACK is transmitted to enable thetransmitter to retransmit the corresponding packet. This operation iscalled ARQ (automatic request).

The ARQ operation can be combined with channel coding scheme. Inparticular, the above-mentioned ARQ is proposed as HARQ (hybrid ARQ)which raises efficiency of whole system in a manner of lowering an errorrate by combining a retransmitted packet with a previously transmittedpacket. In order to raise throughput of system, the HARQ is requested toreceive an ACK/NACK response faster than that of the conventional ARQoperation from a receiver. Hence, ACK/HACK is transmitted by physicalchannel signaling in HARQ.

Implementations of HARQ can be categorized into two types. A first typeis chase combining (CC), in which retransmission is performed using thesame code bits by the same modulation scheme and coding rate as that ofa previously packet. A second type is incremental redundancy (IP), inwhich retransmission is performed in a manner of allowing a transmissionby using a modulation scheme and coding rate different from those of thepreviously transmitted packet. In this case, the receiver can raise thethroughput of system through coding diversity.

In a multi-carrier cellular module communication system, user equipmentsbelonging to one or a plurality of cells perform uplink data packettransmission to a base station. Since a plurality of user equipments areable to transmit uplink data packets within a single subframe, a basestation should be able to transmit ACK/NACK signals to a plurality ofthe user equipments within the single subframe. In particular, in the3GPP LTE system, a base station transmits ACK/NACK signals to aplurality of user equipments via a physical HARQ indicator channel(hereinafter abbreviated PHICH), and more particularly, via a channelfor transmitting downlink ACK/NACK information for uplink HARQ.

In case that a base station multiplexes a plurality of ACK/NACK signalstransmitted to user equipments within a single subframe by CDMA in apartial time-frequency domain of a downlink transmission band of amulti-carrier system, the multiplexed signals are discriminated fromACK/NACK signals for other user equipments by orthogonal orpseudo-orthogonal code multiplied through the time-frequency domain.Moreover, in case of performing QPSK transmission, the discriminationcan be achieved through two different orthogonal phase components. Inparticular, a plurality of ACK/NACK signals are transmitted by beingmultiplexed by CDMA through a plurality of PHICHs in the 3GPP LTEsystem. And, a unit of the transmission through the multiplexing by CDMAis called ‘PHICH group’.

Meanwhile, in case that a specific user equipment tries an initialaccess to a prescribed cell, the user equipment needs to acquire systeminformation of the corresponding cell. Such basic information e.g.system bandwidth can be received via a physical broadcast channel(hereinafter abbreviated ‘PBCH’). Yet, in order to acquire detailedsystem information from the system information of the correspondingcell, the user equipment is requested to receive a physical downlinkshared channel (hereinafter abbreviated ‘PDSCH’) that is the channel fortransmitting general downlink data.

In this case, scheduling information of PDSCH is transmitted via PDCCHof each subframe. A user equipment in progress of an initial accessreceives PBCH and then receives PDCCH of a specific subframe. Hence, theuser equipment is able to know scheduling information on PDSCHtransmitting detailed system information through that subframe. In thiscase, in order to receive the PDCCH having the scheduling informationabout the PDSCH transmitting the detailed system information, atransmission location of the corresponding PDCCH should be known.

Since PDCCH is generally mapped to RE (Resource Element) except RE(s)for carrying PHICH and other control signals, it should be checked howthe PHICH and other control signals are mapped to a resource region toreceive the PDCCH.

DISCLOSURE OF THE INVENTION Technical Problem Technical Solution

Accordingly, the present invention is directed to a method of acquiringresource region information for PHICH in a mobile communication systemand a method of receiving a physical downlink control channel (PDCCH)using the same that substantially obviate one or more of the problemsdue to limitations and disadvantages of the related art.

An object of the present invention is to provide a method of acquiringresource region information for PHICH in a mobile communication systemand a method of receiving a physical downlink control channel (PDCCH)using the same, by which location information of a resource region fortransmitting PHICH is efficiently transferred and by which an initialaccess user equipment is facilitated to receive PDCCH.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a method ofacquiring PHICH transmission resource region information, in which auser equipment (UE) acquires resource region information fortransmitting PHICH (physical hybrid ARQ indicator channel), according tothe present invention includes the steps of, receiving a PBCH (physicalbroadcast channel), and acquiring the resource region information fortransmitting the PHICH according to information of the received PBCH,wherein the resource region for transmitting the PHICH is determinedaccording to a first information corresponding to the number (N) ofPHICH per subframe and a second information corresponding to a duration(m) of the PHICH per subframe, wherein the first information isdetermined as a value resulting from multiplying a basic numberpredetermined according to a system bandwidth by a specific constant,and wherein the specific constant is acquired from the information ofthe received PBCH.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, a method of receiving a PDCCH, inwhich a user equipment (UE) receives a physical downlink control channel(PDCCH), includes the steps of receiving a PBCH (physical broadcastchannel), acquiring resource region information for transmitting a PHICH(physical hybrid ARQ indicator channel) according to information of thereceived PBCH, and receiving the PDCCH according to the resource regioninformation for transmitting the PHICH, wherein the resource region fortransmitting the PHICH is determined according to a first informationcorresponding to the number (N) of PHICH per subframe and a secondinformation corresponding to a duration (m) of the PHICH per subframe,wherein the first information is determined as a value resulting frommultiplying a basic number predetermined according to a system bandwidthby a specific constant, and wherein the specific constant is acquiredfrom the information of the received PBCH.

Preferably, the first information includes either number information ofthe PHICH per subframe or number information of PHICH group persubframe. Preferably, the second information is acquired from theinformation of the received PBCH.

More preferably, the PBCH includes signaling information for indicatingthe duration (m) information of the PHICH per subframe. In this case,the signaling information can have a 1-bit length. More preferably, thespecific constant includes one selected from the group consisting of ⅙,½, 1 and 2.

Preferably, the PDCCH is received a resource region except the resourceregion for transmitting the PHICH within a prescribed OFDM symbolinterval from a first OFDM symbol of each subframe and the PDCCHreceiving step includes the step of enabling the user equipment todecode the resource region except the resource region for transmittingthe PHICH within the prescribed OFDM symbol interval as a PDCCH searchregion.

To further achieve these and other advantages and in accordance with thepurpose of the present indention, a method of transferring PHICH(physical hybrid ARQ indicator channel) transmission resource regioninformation, includes the step of transmitting a PBCH (physicalbroadcast channel) including specific constant information, wherein theresource region for transmitting the PHICH is determined according to afirst information corresponding to the number (N) of PHICH per subframeand a second information corresponding to a duration (m) of the PHICHper subframe and wherein the first information is determined as a valueresulting from multiplying a basic number (e.g., a basic PHICH number ora basic PHICH group number) predetermined according to a systembandwidth by the specific constant.

Preferably, the first information includes either number information ofthe PHICH per subframe or number information of PHICH group persubframe. Preferably, the PBCH includes signaling information forindicating the second information.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

Advantageous Effects

According to the above-described embodiments of the present invention,location information of a resource region for transmitting PHICH isefficiently transferred and an initial access user equipment isfacilitated to receive PDCCH.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a block diagram of a wireless communication system;

FIGS. 2A to 2D are exemplary diagrams to explain the concept of aresource region location for transmitting PHICH and corresponding PDCCHtransmission position according to first information and secondinformation; and

FIG. 3 is a conceptional diagram to explain information relation toenable an initial access user equipment to receive PDICH.

BEST MODE Mode for Invention

Reference will now be mads in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 is a block diagram of a wireless communication system,

A wireless communication system is widely deployed to provide variouscommunication services including voice, packet data and the like,Referring to FIG. 1, a wireless communication system includes a userequipment (UE) 10 and a base station (BS) 20. The user equipment 10 isfixed or can have mobility. And, a terminal can be called such aterminology as a user equipment (UE), a mobile station (MS), a userterminal (UT), a subscriber station (SS) a wireless device and the like.The base station 20 generally means a fixed station and can be calledsuch a terminology as a node B (NodeB), a base transceiver system (BTS),an access point and the like. And, at least one cell can exist for asingle base station 20.

The wireless communication system can be an OFDM/OFDMA (orthogonalfrequency division multiplexing/orthogonal frequency division multipleaccess) based system. The OFDM uses a plurality of orthogonalsubcarriers. The OFDM uses orthogonal characteristic between IFFT(inverse fast Fourier transform) and FFT (fast Fourier transform). Atransmitter transmits data by performing IFFT. A receiver reconstructsoriginal data by performing FFT on a received signal. The transmitteruses IFFT to combine multiplexed subcarriers. And, the receiver usescorresponding FFT to separate the multiplexed subcarriers.

The present invention is intended to provide a method of efficientlytransferring location information of a resource region for transmittingPHICH in the above-described wireless communication system and a methodof facilitating an initial access user equipment to receive PDCCH usingthe same. For this, how to specify a resource region for transmittingPHICH is explained in the first place as follows.

First of all, in the 3GPP LTE system, PHICH is transmitted via first mOFDM symbols among OFDM symbols of each subframe, where m≥1. And, PHICHand other control signals are transmitted via specific resource elements(REs) within first n OFDM symbols of the corresponding subframe, wheren≥m. Meanwhile, PDCCH is transmitted via REs except the former REs forcarrying the above-mentioned PHICH and other control signals within then OFDM symbols of the subframe. Hence, in order to receive schedulinginformation via the PDCCH of each subframe, the user equipment shouldknow how PHICHs are mapped to the corresponding subframe.

Resource region mapping of PHICH in each subframe of each cell can bedetermined by two factors including information corresponding to an Nvalue that is the number of PHICHs existing in the correspondingsubframe and information corresponding to an m value that is the numberof OFDM symbols having the PHICH mapped thereto in the subframe. In thiscase, the number of the OFDM symbols haying the PHICH mapped thereto canbe names a “PHICH duration”. Hence, the user equipment should know thetwo factors to receive the PDCCH of each subframe.

Meanwhile, the PHICH group means a set in which PHICHs are multiplexedby CDMA, In particular, a plurality of PHICHs mapped to a same resourceelement (RE) set construct a PHICH group. In this case, the PHICHswithin the PHICH group can he discriminated from each other by differentorthogonal sequences, respectively. If the number of the PHICH groups isrepresented as the following relation with the number H of PHICHs isestablished,

N=G _(N) *C   [Formula 1]

In Formula 1, ‘C’ indicates the number of orthogonal orpseudo-orthogonal codes used for multiplexing by CDMA. Since a value ofC can be determined fixed according to a system environment, it is ableto obtain the number N of PHICHs according to the number G_(N) of thePHICH groups. Hence, the information corresponding to the number N ofthe PHICHs per subframe can be the value N itself or the value G_(N).

In brief, a location of a resource region for transmitting PHICH can bedetermined by the number N of PHICHs per subframe or the per-subframePHICH group information (hereinafter named first ‘information’)corresponding to the number N and the OFDM symbol number value m(hereinafter named ‘second information’) having the PHICH per subframemapped thereto. In case that the transmission resource region locationof the PHICH is determined based on the above informations, it is ableto determine a location of the transmission resource region of thePDCCH.

FIGS. 2A to 2D are exemplary diagrams to explain the concept of aresource region location for transmitting PHICH and corresponding PDCCHtransmission position according to first information and secondinformation.

In FIG. 2A and FIG. 2B, shown are the case that a PHICH duration m is 1or 3 in case that an OFDM symbol interval n for control informationtransmission within a subframe is 3 and that the number of PHICH groupsis 2. FIG. 2C and FIG. 2D show the case of m=1 and G_(N)=2 in case thatn is 2 or 1. Referring to FIGS. 2A to 2D, if the first information suchas N or G_(N) and the second information corresponding to m arespecified, a resource region for transmitting PHICH can be obtainedaccording to a predetermined pattern. Hence, it is able to obtain aposition for transmitting PDCCH within an OFDM symbol region within arange of n.

In the following description of an embodiment, a method of announcingthe first and second informations efficiently is explained. Prior tolooking into the method of transferring the PHICH transmission regioninformation efficiently, it is necessary to review the relation betweeninformations required for a reception of each channel.

FIG. 3 is a conceptional diagram to explain information relation toenable an initial access user equipment to receive PDSCH.

First of all, an initial access user equipment is able to acquire basicsystem information by receiving PBCH [S301]. Yet, as mentioned in theforegoing description, in order to acquire detailed system information,a reception of PDSCH is necessary [S302]. Meanwhile, since schedulinginformation of the PDSCH is transmitted via PDCCH of each subframe, forthe PDSCH reception [S302], a reception [S303] of the PDCCH isnecessary. Besides, since the PDCCH, as shown in FIG. 2, is transmittedvia a region except the transmission region of the PHICH and othercontrol information within the n-OFDM symbol range of each subframe,acquisition [S304] of information on the PHICH transmission regionwithin the subframe is necessary.

Meanwhile, the PHICH transmission region, as mentioned in the foregoingdescription with reference to FIG. 2, can be determined via the firstinformation and the second information.

It can fee observed from FIG. 3 that the initial access user equipmentis facilitated to acquire the first information and the secondinformation in a manner of transmitting the first and/or secondinformation via PBCH. Therefore, a method of transmitting firstinformation via PBCH according to one embodiment of the presentinvention is proposed. In case that the first information is transmittedvia PBCH, the transmitted information can correspond to the number N ofPHICHs per subframe or the PHICH group number G_(N).

Meanwhile, a method of determining first information according to asystem bandwidth in advance is available as well. For instance, in casethat L RBs (resource blocks) exist within a system band of a prescribedcell, PHICH information on a data transmission via each of the RBs canbe transmitted in downlink. In this case, L PHICHs corresponding to theRB number within the system band can be set to a basic N in eachdownlink subframe. If so, it is unnecessary to transmit a value of the Nto a user equipment separately. Alternatively, by defining the G_(N)value corresponding to the number of PHICH groups instead of the Nvalue, the same effect as defining the N value can be obtained.

In this case, the following items can be taken into consideration. Forinstance, in case that multi-user MIMO transmission or single-user MIMOtransmission is possible in uplink, the number of necessary downlinkPHICHs can be incremented into the multiplications amounting to adifference possible for spatial multiplexing in uplink. When data aretransmitted in uplink via several RBs, it is unnecessary to transmitPHICH information on all RBs in downlink. Hence, the number of PHICHsmay be decremented. Therefore, another embodiment of the presentinvention proposes a method of determining the number of basic PHICHsdetermined in advance according to a system bandwidth (or the basicPHICH group number) and then announcing a ratio of the number of thebasic PHICHs (or the basic PHICH group number) to the number of realPHICHs (or the real PHICH group number) via PBCH, instead oftransmitting the first value via PBCH in direct.

For instance, assume that the basic PHICH group number is determined inadvance according to a system bandwidth and assume that a constantcorresponding to a ration of the basic PHICH group number to the realPHICH group number is transferred via PBCH. Generally, a PHICH groupindicates PHICHs mapped to the same resource element set by orthogonalcode. In case of the 3GPP LTE system, the number of PHICHs mapped to asingle PHICH group can be 8 or 4. In particular, in case of using ageneral CP, eight PHICHs can be mapped to a single PHICH group. In caseof using an extended CP, four PHICHs can be mapped to a single PHICHgroup.

For instance, assuming that a downlink bandwidth indicated by afrequency domain RB unit in a subframe using a general CP is set toN_(RB) ^(DL), the number of PHICH groups can be represented as Formula 2or Formula 3.

G_(N)=a┌N_(RB) ^(DL)/8┐  [Formula 2]

G_(N)=┌a·N_(RB) ^(DL)/8┐  [Formula 3]

In Formula 2 and Formula 3 , ┌x┐ indicates an integer equal to orgreater than x. In Formula 2 and Formula 3, ‘a’ is a constantcorresponding to a ratio the basic PHICH group number (┌N_(RB) ^(DL)/8┐or N_(RB) ^(DL)/8) determined in advance according to a system bandwidthto the real PHICH group number GN and is assumed as transmitted via PBCHin the present embodiment. For instance, the ‘a’ can be one of ⅙, ½, 1or 2. Yet, the ‘a’ may correspond to another value according to a systemrequirement. Moreover, Formula 2 and Formula 3 are exemplary for thecase of using the general CP. In case of using the extended CP, twotimes of the basic PHICH group number can be used for the calculation ofthe real PHICH group number G_(N).

Meanwhile, in order to secure a PDCH transmission position, secondinformation corresponding to a PHCH duration m needs to be secured aswell as first information corresponding to the PHICH transmission numberN or the PHICH group number G_(N).

According to one embodiment of the present invention for the secondinformation, proposed is a method of transferring the second informationvia signaling information of PBCH like the first information. If a valuem, as shown in FIG. 2, is set to either 1 or 3, it is able to transferthe second information to a user equipment via 1-bit signaling of PBCH.Moreover, it is able to set to indicate that the value m corresponds toeither 1 or 2 via the same 1-bit signaling as well.

According to another embodiment of the present invention, proposed is amethod of defining a value m to be determined in advance according to avalue N per bandwidth in case that the number (value N) of PHICHallocation varies within a single bandwidth. For instance, in case thatthe value N is allocated different as 1 to 50 in a system having abandwidth of 10 MHz, if a value N is equal to or greater than 1 andequal to or smaller than 25, it is able to define m=1 in advance. If thevalue N is equal to or greater than 26 and equal to or smaller than 50,it is able to define m=2 in advance. If so, a user equipment is able toknow a value m through the value N without transmitting a value mseparately.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

INDUSTRIAL APPLICABILITY

Accordingly, a method of transferring PHICH transmission resource regioninformation and a PDCCH receiving method using the same according to therespective embodiments of the present invention is applicable to the3GPP LTE system. Yet, the principle for a user equipment applied to thepresent invention to receive each channel information and the principlefor acquiring information necessary for the same are applicable to otherwireless communication systems.

What is claimed is:
 1. A method for a user equipment (UE) to receive aphysical downlink control channel (PDCCH) signal transmitted from a basestation (BS) via a specific resource region, the method comprising:receiving a physical broadcast channel (PBCH) signal comprising: firstinformation related to a system bandwidth, second information related toa specific constant for physical hybrid ARQ indicator channel (PHICH),and third information related to a duration of PHICH, wherein theduration of PHICH indicates a number of orthogonal frequency divisionmultiplexing (OFDM) symbols to which a PHICH is mapped; determining avalue by multiplying a basic number predetermined according to thesystem bandwidth by the specific constant for PHICH; determining aresource region used for PHICH transmission based on the determinedvalue and the duration of PHICH; and receiving the PDCCH signal from theBS via the specific resource region for downlink control information,wherein the specific resource region is determined among resourceregions not being used for the PHICH transmission, and wherein thespecific resource region is within a resource region having a prescribednumber of OFDM symbols that is equal to or greater than the number ofOFDM symbols corresponding to the duration of PHICH in a time domainstarting from a first OFDM symbol of each subframe.
 2. The method ofclaim 1, wherein the specific constant comprises a positive integer. 3.A user equipment (UE) configured to receive a physical downlink controlchannel (PDCCH) signal transmitted from a base station (BS) via aspecific resource region, the UE comprising: a radio frequency (RF) unitconfigured to: a processor operatively connected to the RF unit andconfigured to: receive a physical broadcast channel (PBCH) signalcomprising: first information related to a system bandwidth, secondinformation related to a specific constant for physical hybrid ARQindicator channel (PHICH), and third information related to a durationof PHICH, wherein the duration of PHICH signal indicates a number oforthogonal frequency division multiplexing (OFDM) symbols to which aPHICH is mapped; determine a value by multiplying a basic numberpredetermined according to the system bandwidth by the specificconstant; determine a resource region used for PHICH transmission basedon the determined value and the duration of PHICH; and receive the PDCCHsignal from the BS via the specific resource region for downlink controlinformation, wherein the specific resource region is determined amongresource regions not being used for the PHICH transmission, and whereinthe specific resource region is within a resource region having aprescribed number of OFDM symbols that is equal to or greater than thenumber of OFDM symbols corresponding to the duration of PHICH in a timedomain starting from a first OFDM symbol of each subframe.
 4. The UE ofclaim 3, wherein the specific constant comprises a positive integer.